This invention relates generally to a power transfer mechanism adapted to be incorporated in a multiple path drive system, for example a four-wheel drive vehicle. More particularly, it relates to a torque transfer case adapted to receive torque from a prime mover and to provide torque for one drive axle where two-wheel drive is adequate, and to provide torque for both drive axles automatically where four-wheel drive is required. The torque transfer case incorporates a double-acting overrunning clutch responsive to relative rotation between the drive axles for automatically engaging where four-wheel drive is required.
In recent years there have been many improvements in automotive drive trains, including improvements relating to the transfer of torque from a prime mover to drive axles. Where four-wheel drive systems are used, transfer cases have been developed which generally provide torque transfer to one output to drive an axle and to another output for driving another axle. Some such transfer cases generally have included an overrunning mechanism which automatically engages and disengages the four-wheel drive function by biasing the cage of the mechanism to ground. However, there remains a need to provide an improved torque transfer case which engages and disengages automatically, but which prevents undesirable engagement should an excessive overrunning condition be encountered.